1. Field of the Invention
The present invention relates to a p-n junction-type compound semiconductor light-emitting device using a group III nitride semiconductor layer containing indium as a light-emitting layer. Specifically, the present invention relates to a p-n junction-type compound semiconductor light-emitting device where an evaporation-preventing layer provided on the light-emitting layer in order to prevent the evaporation of indium from the light-emitting layer is composed of an indirect transition-type boron phosphide (BP)-base semiconductor of a first or a second conduction type.
2. Background Art
Group III nitride semiconductors containing indium, such as gallium indium nitride (GaXIn1xe2x88x92XN: 0xe2x89xa6Xxe2x89xa61) (indium-containing group III nitride semiconductor), have been heretofore used as a constituent material of a light-emitting layer for emitting short wavelength light such as blue light (see, JP-B-55-3834 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d)). In order to obtain high-intensity light emission, the light-emitting part usually assumes a double hetero (DH) structure consisting of a light-emitting layer and barrier layers (cladding layers) sandwiching the light-emitting layer. The cladding layer for a GaXIn1xe2x88x92XN (0xe2x89xa6Xxe2x89xa61) light-emitting layer is conventionally composed of a group III nitride semiconductor such as wurtzite crystal-structure aluminum gallium nitride (AlXGa1xe2x88x92XN: 0xe2x89xa6Xxe2x89xa61) intentionally doped with an n-type or a p-type impurity (see, JP-A-6-283825 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)).
However, in a high temperature environment, indium (In) in the GaXIn1xe2x88x92XN (0xe2x89xa6Xxe2x89xa61) layer evaporates significantly and the indium composition (=1xe2x88x92X) in the layer decreases. In conventional techniques, an xe2x80x9cevaporation-preventingxe2x80x9d layer for preventing the evaporation of indium is formed on the GaXIn1xe2x88x92XN (0xe2x89xa6Xxe2x89xa61) light-emitting layer, and a cladding layer such as gallium nitride (GaN) is then provided in a high temperature environment (see, JP-A8-293643). The xe2x80x9cevaporation-preventingxe2x80x9d layer was heretofore exclusively composed of a group III nitride semiconductor such as direct transition-type wurtzite crystal-structure aluminum gallium nitride (AlXGa1xe2x88x92XN: 0xe2x89xa6Xxe2x89xa61) (see, JP-A-5-69236 and JP-A-8-293643).
A technique where a xe2x80x9cdiffusion-preventingxe2x80x9d layer for preventing the impurity doped in the barrier layer from diffusing and penetrating into the light-emitting layer or xe2x80x9cevaporation-preventingxe2x80x9d layer is provided between the xe2x80x9cevaporation-preventingxe2x80x9d layer and the barrier layer is also disclosed (see, JP-A-6-283825, supra). In particular, the xe2x80x9cdiffusion-preventingxe2x80x9d layer for preventing magnesium (Mg) from diffusing and penetrating inside the n-type GaXIn1xe2x88x92XN light-emitting layer from the Mg-doped p-type barrier layer is usually also composed of a group III nitride semiconductor such as direct transition-type aluminum gallium nitride (AlXGa1xe2x88x92XN: 0xe2x89xa6Xxe2x89xa61) (see, (1) JP-A-6-283825 supra and (2) JP-A-2001-36196).
Problems in conventional techniques regarding the xe2x80x9cevaporation-preventingxe2x80x9d layer are attributable to the wurtzite crystal-structure aluminum gallium nitride (AlXGa1xe2x88x92XN: 0xe2x89xa6Xxe2x89xa61) constituting the xe2x80x9cevaporation-preventingxe2x80x9d layer. The wurtzite-structure crystal has a peculiar non-degenerated valence band structure (see, Toshiaki Ikoma and Hideaki Ikoma, Kagobutsu Handotai no Kiso Bussei Nyumon (Guide for Basic Physical Properties of Compound Semiconductor), 1st ed., page 17, Baifukan (Sep. 10, 1991)) and is conduction cannot be readily formed. For obtaining a low-resistance p-type group III nitride semiconductor layer, the wurtzite-structure crystal must be subjected to a heat treatment so as to eliminate a hydrogen atom (proton) (see, JP-A-5-183189). When an xe2x80x9cevaporation-preventingxe2x80x9d layer to be disposed between a barrier layer and a light-emitting layer composed of an indium-containing group III nitride semiconductor cannot be readily constructed on the light-emitting layer from a low-resistance electrically conducting layer, for example, a light-emitting diode (LED) having a low forward voltage (so-called Vf) cannot be readily provided. In addition, a laser diode (LD) having a low threshold voltage (so-called Vth) cannot be readily provided.
In a direct transition-type semiconductor, the probability of radiative recombination which brings about light emission is by far higher than that in an indirect transition-type semiconductor (see, K. Seeger, Semiconductor no Butsuri Gaku (Ge) (Physics of Semiconductor (Last Volume))xe2x80x9d, 1st imp., page 507, Yoshioka Shoten (Jun. 25, 1991)). This is the reason why the light-emitting layer is preferentially composed of a direct transition-type semiconductor material. In conventional techniques, the xe2x80x9cevaporation-preventingxe2x80x9d layer is, however, also composed of a direct transition-type group III nitride semiconductor having a high probability of radiative recombination. In addition to light emission from the light-emitting layer composed of an indium-containing group III nitride semiconductor, light is therefore also generated from the xe2x80x9cevaporation-preventingxe2x80x9d layer itself. In other words, light emission of a single wavelength cannot be obtained, and this disturbs the fabrication of a light-emitting device having excellent monochromaticity.
In conventional techniques, a barrier layer provided above the xe2x80x9cevaporation-preventingxe2x80x9d layer is also composed of a group III nitride semiconductor intentionally doped with an impurity. For example, the barrier layer on the light-emitting layer is composed of a magnesium (Mg)-doped group III nitride semiconductor. Therefore, it has been heretofore necessary to provide a xe2x80x9cdiffusion-preventingxe2x80x9d layer for preventing the penetration of impurity such as Mg from the barrier layer into the light-emitting layer. That is, a light-emitting device cannot be readily fabricated.
The present invention has been made to solve the above-described problems. Specifically, the above object of the present invention has been achieved by providing the following:
(1) a p-n junction-type compound semiconductor light-emitting device comprising a substrate composed of a single crystal, a first barrier layer provided on the substrate and composed of a compound semiconductor of a first conduction type, a light-emitting layer provided on the first barrier layer and composed of an indium (In)-containing group III nitride semiconductor of a first or a second conduction type, and an evaporation-preventing layer provided on the light-emitting layer for preventing the evaporation of indium from the light-emitting layer, wherein the evaporation-preventing layer is composed of an undoped boron phosphide (BP)-base semiconductor of second conduction type;
(2) the p-n junction-type compound semiconductor light-emitting device as described in (1) above, wherein the evaporation-preventing layer almost lattice-matches with the light-emitting layer;
(3) the p-n junction-type compound semiconductor light-emitting device as described in (1) or (2) above, wherein the first barrier layer is composed of an undoped boron phosphide-base semiconductor where an impurity is not intentionally added;
(4) a p-n junction-type compound semiconductor light-emitting device comprising a substrate composed of a single crystal, a first barrier layer provided on the substrate and composed of a compound semiconductor of a first conduction type, a light-emitting layer provided on the first barrier layer and composed of an indium (In)-containing group III nitride semiconductor of a first or a second conduction type, an evaporation-preventing layer provided on the light-emitting layer for preventing the evaporation of indium from the light-emitting layer, and a second barrier layer provided on the evaporation-preventing layer and composed of a compound semiconductor of a second conduction type, wherein the evaporation-preventing layer is composed of an undoped indirect transition-type boron phosphide (BP)-base semiconductor of a first or a second conduction type;
(5) the p-n junction-type compound semiconductor light-emitting device as described in (4) above, wherein the evaporation-preventing layer almost lattice-matches with the light-emitting layer;
(6) the p-n junction-type compound semiconductor light-emitting device as described in (4) or (5) above, wherein the first barrier layer is composed of an undoped boron phosphide-base semiconductor where an impurity is not intentionally added;
(7) the p-n junction-type compound semiconductor light-emitting device as described in any one of (4) to (6) above, wherein the second barrier layer is composed of an undoped boron phosphide-base semiconductor where an impurity is not intentionally added;
(8) a lamp fabricated using the p-n junction-type compound semiconductor light-emitting device described in any one of (1) to (7) above;
(9) a light source using the lamp described in (8) above;
(10) a method for producing a p-n junction-type compound semiconductor light-emitting device, which comprises forming a first barrier layer composed of a compound semiconductor of a first conduction type on a substrate composed of a single crystal, forming a light-emitting layer composed of an indium (In)-containing group III nitride semiconductor of a first or a second conduction type on the first barrier layer, and forming an evaporation-preventing layer on the light-emitting layer for preventing the evaporation of indium from the light-emitting layer, wherein the evaporation-preventing layer is composed of an undoped boron phosphide (BP)-base semiconductor of a second conduction type;
(11) the method for producing a p-n junction-type compound semiconductor light-emitting device as described in (10) above, wherein the first barrier layer, the light-emitting layer and the evaporation-preventing layer are formed by a metal organic chemical vapor deposition method (MOCVD method);
(12) a method for producing a p-n junction-type compound semiconductor light-emitting device, which comprises forming a first barrier layer composed of a compound semiconductor of a first conduction type on a substrate composed of a single crystal, forming a light-emitting layer composed of an indium (In)-containing group III nitride semiconductor of a first or a second conduction type on the first barrier layer, forming an evaporation-preventing layer on the light-emitting layer for preventing the evaporation of indium from the light-emitting layer, and forming a second barrier layer composed of a compound semiconductor of a second conduction type on the evaporation-preventing layer, wherein the evaporation-preventing layer is composed of an undoped indirect transition-type boron phosphide (BP)-base semiconductor of a first or a second conduction type; and
(13) the method for producing a p-n junction-type compound semiconductor light-emitting device as described in (12) above, wherein the first barrier layer, the light-emitting layer, the evaporation-preventing layer and the second barrier layer are formed by a metal organic chemical vapor deposition method (MOCVD method).